Message-ID: <20230531144258.GB24749@pendragon.ideasonboard.com>
Date:   Wed, 31 May 2023 17:42:58 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Tommaso Merciai <tomm.merciai@...il.com>
Cc:     jacopo.mondi@...asonboard.com, martin.hecht@...et.eu,
        linuxfancy@...glegroups.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Gerald Loacker <gerald.loacker@...fvision.net>,
        Nicholas Roth <nicholas@...hemail.net>,
        Shawn Tu <shawnx.tu@...el.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Benjamin Mugnier <benjamin.mugnier@...s.st.com>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH v2 2/2] media: i2c: Add support for alvium camera

Hi Tommaso,

On Wed, May 31, 2023 at 04:19:03PM +0200, Tommaso Merciai wrote:
> On Wed, May 31, 2023 at 02:33:31PM +0300, Laurent Pinchart wrote:
> > On Wed, May 31, 2023 at 12:13:39PM +0200, Tommaso Merciai wrote:
> > > On Mon, May 29, 2023 at 10:40:18AM +0300, Laurent Pinchart wrote:
> > > > On Fri, May 26, 2023 at 07:39:44PM +0200, Tommaso Merciai wrote:
> > > > > The Alvium camera is shipped with sensor + isp in the same housing.
> > > > 
> > > > What ISP is that ?
> > > 
> > > The isp comes from Allied Vision, is called Alvium and is part of the camera.
> > > In real is a vision processor, this offers more functionality then an isp can do.
> > > It is not sold separately but is an integrated part of the camera itself
> > > which also takes care of the sensor abstraction.
> > > 
> > > > > The camera can be equipped with one out of various sensor and abstract
> > > > > the user from this. Camera is connected via MIPI CSI-2.
> > > > > 
> > > > > Most of the sensor's features are supported, with the main exception
> > > > > being fw update.
> > > > 
> > > > I assume you mean "camera module features" here, as firmware update
> > > > isn't a camera sensor feature.
> > > 
> > > Yep.
> > > 
> > > > > The driver provides all mandatory, optional and recommended V4L2 controls
> > > > > for maximum compatibility with libcamera
> > > > > 
> > > > > References:
> > > > >  - https://www.alliedvision.com/en/products/embedded-vision-solutions
> > > > 
> > > > I'll do a partial review only as the patch is large, and will try to
> > > > review the rest in v2.
> > > 
> > > No problem.
> > > 
> > > > > Signed-off-by: Tommaso Merciai <tomm.merciai@...il.com>
> > > > > ---
> > > > >  drivers/media/i2c/Kconfig  |    9 +
> > > > >  drivers/media/i2c/Makefile |    1 +
> > > > >  drivers/media/i2c/alvium.c | 3547 ++++++++++++++++++++++++++++++++++++
> > > > >  drivers/media/i2c/alvium.h |  500 +++++
> > > > >  4 files changed, 4057 insertions(+)
> > > > >  create mode 100644 drivers/media/i2c/alvium.c
> > > > >  create mode 100644 drivers/media/i2c/alvium.h

[snip]

> > > > > diff --git a/drivers/media/i2c/alvium.c b/drivers/media/i2c/alvium.c
> > > > > new file mode 100644
> > > > > index 000000000000..e77fb6bda64b
> > > > > --- /dev/null
> > > > > +++ b/drivers/media/i2c/alvium.c
> > > > > @@ -0,0 +1,3547 @@

[snip]

> > > > > +static int alvium_set_streamon_delay(struct alvium_dev *alvium)
> > > > > +{
> > > > > +	struct device *dev = &alvium->i2c_client->dev;
> > > > > +	int ret;
> > > > > +	u64 streamon_delay;
> > > > > +
> > > > > +	if (!alvium->bcrm_addr)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	/*
> > > > > +	 * CSI2 receivers sometimes need some delay before are ready to
> > > > > +	 * get data. This register set delay before camera start
> > > > > +	 * capturing frames in us.
> > > > 
> > > > If the CSI-2 receiver needs a delay, it should be handled by the CSI-2
> > > > receiver driver, not here.
> > > 
> > > My bad, bad description/bad name.
> > > 
> > > This regs is an optional delay that alvium introduces between switching
> > > from lp to hs mode.
> > > Some mipi receivers require this delay on the sender side.
> > > 
> > > I plan to switch to the following name: alliedvision,lp2hs-delay-us
> > > and fix the comment with the above comment^
> > > 
> > > This is more clear, what do you think about?
> > 
> > It's a bit clearer, but still not fully :-) Does this delay correspond
> > to one of the MIPI D-PHY timing parameters ? If so, which one ?
> 
> Thanks to Martin Hecht I'm able to provide you a clearer description:
> 
> Alvium normally delivers a continous clock even when it is not streaming.

That's an interesting design choice.

> The purpose of this reg is force a DPhy reset for the period described by
> the us on the reg before it starts streaming. To be clear, with that value
> bigger than 0 the Alvium forces a dphy-reset on all lanes for that period.
> That means all lanes go up into low power state.
> This may help a csi2 rx ip to reset if that IP can't deal with a continous clock.

No CSI-2 receiver can possibly handle this :-) If the camera power can't
be turned on only after the CSI-2 receiver is started (as obviously the
camera can't output a HS clock when it's not powered on), then the
receiver wouldn't be able to synchronize.

Thanks for the explanation. Could you record this in the DT bindings ?

> > > > > +	 */
> > > > > +	streamon_delay = (u64)alvium->streamon_delay;
> > > > > +
> > > > > +	ret = alvium_i2c_write_reg_hshake(alvium,
> > > > > +				  alvium->bcrm_addr +
> > > > > +				  REG_BCRM_STREAM_ON_DELAY_32RW,
> > > > > +				  4, streamon_delay);
> > > > > +	if (ret) {
> > > > > +		dev_err(dev, "Fail to set streamon delay reg\n");
> > > > > +		return ret;
> > > > > +	}
> > > > > +
> > > > > +	return 0;
> > > > > +}

[snip]

-- 
Regards,

Laurent Pinchart

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